Saturday, April 6, 2013

Fitness II Target levels (aerobic)

How much do you need to work out? It's an interesting question. The short answer from Thomas and Wing (2009) is 1 hour a day of walking, or 200 minutes a week. Looking a little deeper, the 1 hour of walking is based off a finding that in the National Weight Control Registry, the average woman burns 2545 calories a week through exercise and the average man burns 3293. (Wing & Phelan 2005).

It's true that over 3/4 of the NWCR maintainers walk as their primary form of exercise, but most use more than one form of exercise, and cycling and weights were used by over 20% of respondents. I think rather than set the perhaps daunting goal of dedicating an hour a day to walking, it's better to encourage people to consider a variety of exercises that meet the calorie goal, and multiple modes of exercise are in keeping with the survey findings.

Hopefully you are using a fitness tracker. They are available on Sparkpeople, fitbit, myfitnesspal, and a number of other websites generally on a free basis with ads. Motion sensing video game consoles and smartphone apps are other means to track fitness.

The 200 minutes figure comes from Jakicic (2003), and looking closer at that study I saw that the 200 minutes were only required to be in bouts of 10 minutes at a time. There is ongoing debate about this, with some people saying aerobic exercise needs to happen in 20 minute bouts, but the total amount of work being done was what most predictive of successful weight management in this study. 200 minutes, which was the maximum exercise "dose" prescribed in this study, was also associated with greater cardiovascular fitness. Would ever more fitness prove even better? For me, I think 45 minutes a day is the longest I'd be interested in working out, though participation in dance, sports, and leisure activities are certainly possibilities, but there's only so much time I can put into working out at this stage in my life.

Another key predictor the NWCR has identified in their maintainers is that they watch much less TV than the average American, and Thomas and Wing (2009) theorize that this gives them more time for exercise, monitoring food intake and other weight related strategies. The average amount of TV watched by an NWCR maintainer was 6 to 10 hours vs. the national average of 28 hours. I'm already in the lower range, though I also will march in place while watching TV, especially during commercial breaks. It does not burn as many calories as actual walking (according to my tracking device), but it beats sitting down.

Finally, it is important to remember that the vast majority of calories we burn are not from working out, but from our metabolism. For myself (at 160 and 67.5 inches) I might burn 450 calories in a day exercising, but I burn over 1700 calories in the same day just keeping my temperature at 98.6 and breathing, eating, and my various less intense activities. The thing is, if I weren't exercising, this larger proportion of calorie burn would start to diminish. There is a post exercise boost to the metabolism that can extend for many hours after exercise.(Knab et al. 2011) Exercise is also necessary to preserve and build lean body mass, which is the topic for the third Fitness installment.

Action Step: Find out how many calories you burn (based on your weight) walking briskly for one hour. This can be done on one of the nutrition trackers mentioned above. If you are interested in other forms of exercise, you can also look into how much time it would take to burn that number of calories in the other exercise. Weight training is a different story, which will be covered in the next installment.